Re: DB Performance decreases due to often written/accessed

On Thu, Oct 19, 2006 at 06:19:16PM +0100, Richard Huxton wrote:
> OK - these plans look about the same, but the time is greatly different.
> Both have rows=140247 as the estimated number of rows in tbl_reg. Either
>  you have many more rows in the second case (in which case you're not
> running ANALYSE enough) or you have lots of gaps in the table (you're
> not running VACUUM enough).

Look closer... the actual stats show that the sorts in the second case
are returning far more rows. And yes, analyze probably needs to happen.

> I'd then try putting an index on (attr1,attr2,attr3...attr6) and see if
> that helps reduce time.

With bitmap index scans, I think it'd be much better to create 6 indexes
and see which ones actually get used (and then drop the others).
--
Jim Nasby                                            jim@nasby.net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)